Multi-layered film reflector manufacturing method

ABSTRACT

A method for manufacturing a multi-layered film reflection mirror, in which a desirable shape precision of a reflective wave front can be obtained after locally scraping the multi-layered film, is provided. The method for manufacturing a multi-layered film reflection mirror according to the present invention, in which a multi-layered film which at least two types of substances having different refractive indices respectively are synchronously deposited with a constant periodic length is formed on a substrate, and the multi-layered film on the substrate is locally scraped in order to correct a phase of a reflective wave front in a reflective surface, wherein said multi-layered film has an internal stress of 50 MPa or smaller.

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing amulti-layered film reflection mirror used to soft X-ray opticalapparatuses such as soft X-ray projection exposure apparatuses.

BACKGROUND ART

[0002] Recently, as semiconductor integrated circuits have becomesmaller in size, in order to improve the resolution of the opticalsystem limited by the boundaries of light diffraction, a projectionexposure method utilizing soft X-ray with a wavelength of 11 to 14 nmshorter than a wavelength of ultraviolet light which is conventionallyused, has been developed (for instance, as shown in D. Tichenor, et al.,SPIE 2437(1995) 292). Such method is called an EUV (Extreme Ultraviolet)lithography (hereinafter referred to as an EUV lithography in thefollowing). The EUV lithography has been expected for a futurelithography technique having a resolution of 70 nm or less, which isimpossible of achieving by the conventional lithography using light (awavelength of 190 nm or more).

[0003] Since the refractive indices of materials are nearly 1 in thewavelength band, ordinary optical elements using refraction orreflection cannot be employed. Then, grazing-incidence mirrors whichutilize a total reflection of a mirror having a refractive indexslightly smaller than 1, or multi-layered film reflection mirrors inwhich weak rays reflected by many interfaces of the multi-layered filmare superimposed in phase in order to obtain a high reflectivity, andthe like are utilized. A Mo/Si multi-layered film which aMolybdenum(Mo)-layer and a Silicon (Si)-layer are depositedalternatively enables a reflectivity of 67.5% at a wavelength band inthe vicinity of 13.4 nm for perpendicular incidence, or, a Mo/Bemulti-layered film which a Mo-layer and a Beryllium(Be)-layer aredeposited alternatively enables a reflectivity of 70.2% at a wavelengthband in the vicinity of 11.3 nm for perpendicular incidence (forinstance, as shown in C. Montcalm, Proc. SPIE, Vol. 3331(1998) P.42).

[0004] The EUV lithography apparatus is constructed mainly from a softX-ray source, an illumination optical system, a mask stage, a focusingoptical system, and a wafer stage, and the like. The soft X-ray sourceutilizes a laser plasma light source, a discharge plasma light sourceand a radiation light and the like. The illumination optical system isconstructed from grazing-incidence mirrors which reflect a soft X-rayincident on the reflective surface from an oblique direction,multi-layered reflection mirrors having a reflective surface made of amulti-layered film, and a filter which transmits a soft X-ray at apredetermined wavelength, and the like, and illuminates on a photomaskwith a soft X-ray having a predetermined wavelength. Since transparentsubstance does not exist in the wavelength band of a soft X-ray, areflective mask is utilized as the photomask instead of theconventionally used transmission mask. Circuit patterns formed on thephotomask are focused on a wafer coated with a photoresist by thefocusing optical system constituted by a plurality of multi-layered filmreflection mirrors and the like, and transferred on the photoresist.Here, a soft X-ray is absorbed in the atmosphere and is attenuated sothat all the optical passages are maintained in a predetermined vacuum(for instance, less than 1×10⁻⁵ Torr).

[0005] The focusing optical system is constructed from a plurality ofmulti-layered film reflection mirrors. Since the reflectivities of themulti-layered film reflection mirrors are not 100%, it is preferable tominimize the number of the mirror in order to suppress a loss of aquantity of light. Until now, an optical system constituting 4multi-layered film reflection mirrors (for instance, T. Jewell and K.Thompson, U.S. Pat. No. 5,315,629 and T. Jwell, U.S. Pat. No. 5,063,586)and an optical system constituting 6 multilayered film reflectionmirrors (for instance, D. Williamson, Japanese Unexamined PatentApplication No Hei 9-211332, U.S. Pat. No. 5,815,310) and the like hasbeen reported. Unlike a refractive optical system in which luminous flux(pencil of rays) travels to one direction, the reflective optical systemin which luminous flux travels to one and the opposite directions in theoptical system requires to prevent the shading of luminous flux, so thatit is difficult to heighten a numerical aperture (N.A). Although a 4mirrors optical system enables a N.A. of 0.15 at the most, a 6 mirrorsoptical system makes it possible to constitute an optical system havinga N.A. larger than that of 4 mirrors optical system. Generally, a numberof the mirrors is even so that the mask stage and the wafer stage can bearranged opposite sides of the exposure focusing optical system. Sinceit is necessary to correct the aberration of such exposure focusingoptical system by using limited number of the mirrors, the surface ofeach of the reflection mirrors is machined to aspheric. And, the systemconstitutes a ringfield optical system in which the aberration iscorrected only near a predetermined image height. In order to transferthe entire pattern formed on the photomask to the wafer, the exposure iscarried out with the mask stage and the wafer stage being scanned at acertain speed determined by the magnification of the optical system.

[0006] The exposure focusing optical system for the above-describedexposure apparatus is so called a diffraction limit optical system andthe designed property thereof can be not satisfied unless a waveaberration is sufficiently reduced. As for a target of an allowablevalue of the wave aberration for the diffraction limit optical system,there is a standard in which the root mean square value (RMS) of thewave aberration is within {fraction (1/14)} of the wavelength used inthe system (as shown in M. Born and E. Wolf, Principles of Optics,4^(th) edition Pergamon Press 1970, p.469). This is a condition at whichStrehl strength (a ratio of a maximum point intensity of an opticalsystem having an aberration to that of a stigmatic optical system)becomes 80% or more. An exposure focusing optical system practicallyused for an exposure apparatuses is manufactured to have an aberrationless than such value.

[0007] The EUV lithography technology which has been developed recentlymainly utilizes a wavelength in the vicinity of 13 nm or 11 nm. Thefigure error (FE) allowable for each of the reflection mirrors for thewave front error (WFE) of the optical system is expressed by thefollowing equation:

FE=WFE/2/{square root}{square root over ( )}m(RMS)

[0008] where m is a number of the reflection mirrors constituting theoptical system. And, the reason of the division by 2 is that the errorof 2 times of the figure error is added to the wave front error becauseboth of the incident light and the reflective light are affected by thefigure error respectively. Finally, in the diffraction limit opticalsystem, the figure error (FE) allowable for the each reflection mirroris expressed by the following equation, where λ is a wavelength and m isa number of the reflection mirrors:

FE=λ/28/{square root}{square root over ( )}m(RMS).

[0009] The FE at the wavelength of 13 nm is 0.23 nm RMS in the case ofthe optical system constructed by 4 reflection mirrors, and is 0.19 nmRMS in the case of the optical system constructed by 6 reflectionmirrors.

[0010] However, it is very difficult to manufacture aspheric reflectionmirrors having such high precision, which is the main reason why the EUVlithography can not be in practical use yet. Although the machiningaccuracy for an aspheric surface, which can be achieved by present, isabout 0.4 to 0.5 nm RMS (as shown in C. Gwyn, Extreme UltravioletLithography White Paper, EUV LLC, 1998, p17), it is necessary to improvea machining technique and a measurement technique for an asphericsurface in order to put the EUV lithography in practical use.

[0011] Recently, Yamamoto reported an epoch-making technique which makeit possible to correct the figure error of a multi-layered filmreflection mirror by sub nm order by scraping layer by layer from thesurface of the multi-layered film reflection mirror (as shown in M.Yamamoto, 7^(th) International Conference on Synchrotron RadiationInstrumentation, Berlin Germany, Aug. 21-25, 2000, POS2-189). Theprinciple of the technology will be explained referring to FIG. 8.Supposing the case that from a surface of a multi-layered film which twotypes of substances A and B are deposited alternately with a periodiclength of d, as shown in FIG. 8A, one layer pair is scraped off, asshown in FIG. 8B. In FIG. 8A, the optical path length of one layer pairhaving a thickness of d along a light beam perpendicularly incident tothe surface of the multi-layered film is expressed by OP=nAdA+nBdB.Where dA and dB are thicknesses of the layers respectively, and dA+dB=d.And, nA and nB are refractive indices of the substances A and Brespectively. As shown in FIG. 8B, the optical path length of a parthaving a thickness of d, in which one layer pair is scraped from themost upper surface of the multi-layered film, is expressed by OP′=nd.Where n is a refractive index in vacuum, here n is 1. Accordingly, anoptical pass length of an incident light beam to the scraped part variesby scraping the most upper layer from the multi-layered film. This isoptically equivalent to modify the surface shape by the variation in theoptical length. The variation in the optical path length (that is, thevariation in the surface shape) is expressed by Δ=OP′−OP. Since therefractive index of substance is nearly 1 at a wavelength band of thesoft X-ray, the Δ becomes small value so that the surface shape can beprecisely corrected by using the present method. For instance, the casethat a Mo/Si multi-layered film is used at a wavelength of 13.4 nm isshown. For the perpendicular incidence, d is 6.8 nm, dMo is 2.3 nm, anddSi is 4.5 nm. At the wave length band, the refractive index (nMo) of Mois 0.92 and the refractive index (nSi) of Si is 0.998. On calculation ofa variation in a optical path length by using these values, OP is 6.6nm, OP′ is 6.8 nm, and Δ is 0.2 nm. By scraping one layer having athickness of 6.8 nm, the surface shape can be modified with a precisionof 0.2 nm. Incidentally, in the case of a Mo/Si multi-layered film,since the refractive index of the Si layer is nearly 1, the variation inthe optical path length is mainly dependent on existence ornon-existence of the Mo layer and independent on existence ornon-existence of the Si layer. Accordingly, when the most upper layer isscraped from the multi-layered film, there is no necessary to controlthe thickness of the Si layer precisely. In this case, the thickness ofthe Si layer is 4.5 nm and the scraping process may be stopped on theprocessing way of the Si layer. This means that processing with aprecision of several nm enables to correct the surface shape by 0.2 nmorder.

[0012] Practically, a reflective wave front is measured after forming amulti-layered film, and an amount of the scraped multi-layered film fromthe most upper surface thereof is determined based on the result of themeasurement, followed by the scraping process.

[0013] Here, the reflectivity of the multi-layered film is increased asthe number of layers of the deposited film increases, and is saturatedto be constant beyond a given number of the deposited film. When thenumber of the layers of the deposited films is given so that thereflectivity is saturated enough, the reflectivity will not change evenif the multi-layered film is scraped.

[0014] In general, a multi-layered film has an internal stress, so aMo/Si film and a Mo/Be film used for EUV lithography also has aninternal stress. For instance, it is reported that a Mo/Si multi-layeredfilm has a compressive stress of about −450 MPa and a Mo/Be film has atensile stress of about +400 MPa (P. B. Mirkarini et.al. Proc. SPIE 3331pp. 133-148 (1998)). In the EUV lithography technique, an internalstress in a multi-layered film considerably influences a shape of asubstrate surface on which the multi-layered film is formed.

[0015] As described above, a shape precision required to the reflectionmirrors for the exposure optical system used for the EUV lithography is0.23 to 0.19 nm RMS or less. Even if the substrate of the mirror for theexposure optical system can be processed to have such shape precision,when a conventional Mo/Si multi-layered film or Mo/Be multi-layered filmis formed on the substrate, the shape of the substrate is deformed dueto the internal stress in the formed multi-layered film. The deformationamount which varies by the shape of the substrate considerably exceedsthe required shape precision.

[0016] For instance, when a Mo/Si multi-layered film (periodic length is7.0 nm, Γ is 0.35, 50 layer pair) having an internal stress of −400 MPais formed on one surface of a substrate made of crystal having adiameter of 200 mm and a thickness of 40 mm, the amount of thedeformation in the substrate caused by the formed film exceeds 10 nm.Here, Γ is a division ratio of a layer structure unit, which shows aratio of a thickness of a substance having a larger absorptance to aperiodic length. Here, it is a ratio of a thickness of the Mo layer tothe periodic length of 7.0 nm. The influence of the component whichcontributes the variation in the radius of curvature of the substrateamong the deformation, components, which produces, can be modulated byadjusting the distance between the mirrors with maintaining theinfluence for the imaging property small. However, the deformationcomponent impossible of being modulated by adjusting the distancebetween the mirrors is 1 nm or more thereby to considerably influenceoptical characteristics of the EUV lithography. Therefore, it is thoughtthat the absolute value of the stress in a multi-layered film has to besuppressed less than 50 MPa.

[0017] In order to solve the problem, methods for reducing the stress inthe multi-layered film are proposed, in which the deposit structure unitis a Mo/Ru/Mo/Si structure instead of a Mo/Si structure and an ion beamis irradiated on the surface after forming each Mo layer (M. Shiraishiet. al. Proc. SPIE 3997 pp. 620-627(2000)), and in which the substrateis heated at the film forming, and the like. The former stress reducingmethod proposed by Shiraishi et.al. reports that the stress in themulti-layered film is reduced to +−14 MPa (tensile stress).

[0018] And, another methods are also proposed, in which a Mo/Bemulti-layered film having a certain tensile stress is pre-formed inorder to cancel a deformation caused by a compressive stress in a Mo/Simulti-layered film, resulted in canceling both stress after forming themulti-layered film (P. B. Mirkarini et.al. Proc. SPIE 3331 pp. 133-148(1998)), in which a multi-layered film is also formed on a back surfaceof the substrate to cancel the deformations, and in which, based on thedeformation caused by the stress of the multi-layered film, a substrateis machined to a shape which predicted to be a target shape after thedeformation caused by the formed multi-layered film.

[0019] Although the method for controlling the reflective wave frontproposed by Yamamoto et.al. is very useful, according to the proposal,the multi-layered film is locally scraped off so that the thickness ofthe multi-layered film becomes uneven on the surface of the substrate.As described above, since a multi-layered film has a internal stress ofabout several 100 MPa in general, if the multi-layered film is locallyscraped off, the total stress (stress×thickness) in the multi-layeredfilm on the surface before the scraping process is different from thatafter the scraping process so that the shape of the substrate isdeformed.

[0020] The conventional method for controlling the reflective wave frontby scraping the multi-layered film will be explained referring to FIG.9. As shown in FIG. 9A, a Mo/Si multi-layered film 91 and 95 are formedon the both surfaces of the plane substrate 93 respectively. Because offorming the multi-layered films on both surfaces of the substrate, thedeformation caused by the stress of the multi-layered film on onesurface of the substrate is canceled with the deformation caused by thestress of the multi-layered film on another surface of the substrate sothat the substrate shape is maintained to be plane. The Mo/Simulti-layered film is composed of 50 layer pairs having a periodiclength of 6.8 nm and Γ of 0.35, and 10 layer pairs having a periodlength of 6.8 nm and Γ of 0.1 which are formed on the former formedMo/Si multi-layered film. The multi-layered film is formed by an ionbeam sputtering method. Γ is a division ratio of a layer structure unit,and shows a ratio of a thickness of a substance having a largerabsorptance to a periodic length. Here, it is a ratio of a thickness ofthe Mo layer to the periodic length of 6.8 nm. The reason why 10 layerpairs having Γ of 0.1 are formed on the most upper surface is to improvethe control precision of the wave front subjected to the scrapingprocess for the multi-layered film. By scraping one layer pair from themulti-layered film, the optical path length is lengthened with 0.05 nm,so the reflective wave front is delayed with 0.1 nm at both of incidenceand reflection. The principle has already been described above. So, asshown in FIG. 9B, when scraping a part 97 from the multi-layered film,the shape of the reflective wave front can be controlled with a highshape precision by adjusting the scraping amount in the reflectivesurface. However, since the Mo/Si multi-layered film has a compressivestress of −450 MPa, the thickness of the multi-layered film where thepart of the multi-layered film is scraped locally becomes uneven so thatthe balance between the total stresses (stress×thickness) on the bothsurfaces of the substrate is lost, and the shape of the substratebecomes to be uneven, as shown in FIG. 9C. In the case that a part of aMo/Si multi-layered film is scraped off, the scraped film has acompressive stress so that a part where the scraped film is formed onthe substrate is deformed to concave. As the result, the reflectivesurface is further delayed with larger length than that predicted by theeffect of the scraping , whereby the wave front can not be controlledwith a desirable precision.

[0021] The wave front shape after the multi-layered film is locallyscraped is dependent on not only the change in the optical path lengthof the reflective light due to the scraped multi-layered film, asdescribed above, but also the deformation of the substrate due to theunevenness of the total stress of the multi-layered film. Accordingly,in order to achieve a desirable shape precision of the reflective wavefront by scraping the multi-layered film locally, there is a problemthat it is not enough to determine the scraping amount based on thechange in the optical path length of the reflective light due to thescraped multi-layered film only.

[0022] The present invention has been made to solve the above-describedproblems, and has an object to provide a method for manufacturing for amulti-layered film reflection mirror capable of obtaining a desirablereflection wave front after scraping the multi-layered film.

DISCLOSURE OF THE INVENTION

[0023] A method for manufacturing a multi-layered film reflection mirroraccording to claim 1 of the present invention is provided, in which amulti-layered film which at least two types of substances havingdifferent refractive indices respectively are synchronously depositedwith a constant periodic length is formed on a substrate, and themulti-layered film on the substrate is locally scraped in order tocorrect a phase of a reflective wave front in a reflective surface,wherein said multi-layered film has an internal stress of 50 MPa orless.

[0024] And, it is preferable that the multi-layered film is a film whichMo/Ru/Mo/Si layers are deposited, and an ion beam is irradiated to asurface after forming each Mo layer.

[0025] According to the claim 1 of the present invention, since themulti-layered film which is locally scraped in order to correct a phaseof a reflective wave front has an internal stress of 50 MPa or less, achange in the total stress (stress×film thickness) due to the scrapingof the multi-layered film can be decreased. Therefore, the reflectivewave front can be controlled with a high precision after scraping themulti-layered film.

[0026] A method for manufacturing a multi-layered film reflection mirroraccording to the claim 3 is provided, in which a multi-layered filmwhich at least two types of substances having different refractiveindices respectively are synchronously deposited with a constantperiodic length is formed on a substrate, and the multi-layered film onthe substrate is locally scraped in order to correct a phase of areflective wave front in a reflective surface, wherein a film or amulti-layered film is formed on a back surface of the substrate in orderto produce a deformation of the substrate capable of canceling adeformation of the substrate caused by scraping the multi-layered film.

[0027] According to the claim 3 of the present invention, since a filmor a multi-layered film is formed on a back surface of the substrate inorder to produce a deformation of the substrate capable of canceling adeformation of the substrate caused by scraping the multi-layered film,the shape of the substrate can be kept to the shape prior to thescraping process of the multi-layered film. Therefore, the reflectivewave front can be controlled with a high precision after scraping themulti-layered film.

[0028] A method for manufacturing a multi-layered film reflection mirroraccording to the claim 4 of the present invention, is provided, in whicha multi-layered film which at least two types of substances havingdifferent refractive indices respectively are synchronously depositedwith a constant periodic length is formed on a substrate, and themulti-layered film on the substrate is locally scraped in order tocorrect a phase of a reflective wave front in a reflective surface,wherein a multi-layered film having a approximately same structure asthat of the multi-layered film formed on the surface of the substrate isformed on a back surface of the substrate, and the multi-layered filmformed on the back surface of the substrate is locally scraped atportions correspondent to the portions where the multi-layered film onthe surface of the substrate is locally scraped in order to correct aphase of a reflective wave front with a same thickness as that of thescraped multi-layered film on the surface of the substrate.

[0029] According to the claim 4 of the present invention, the totalstresses on both surfaces of the substrate are canceled so that theshape of the substrate can be kept to the shape prior to the scrapingprocess of the multi-layered film. Therefore, the reflective wave frontcan be controlled with a high precision after scraping the multi-layeredfilm.

[0030] A method for manufacturing a multi-layered film reflection mirroraccording to claim 5 of the present invention is provided, in which amulti-layered film which at least two types of substances havingdifferent refractive indices respectively are synchronously depositedwith a constant periodic length is formed on a substrate, and themulti-layered film on the substrate is locally scraped in order tocorrect a phase of a reflective wave front in a reflective surface,wherein a scraping amount of the multi-layered film is determined basedon an influence of a deformation of the substrate caused by scraping themulti-layered film.

[0031] According to the claim 5 of the present invention, since ascraping amount of the multi-layered film is determined based on aninfluence in a deformation of the substrate caused by scraping themulti-layered film, the reflective wave front can be controlled with ahigh precision after scraping the multi-layered film.

[0032] A method for manufacturing a multi-layered film reflection mirroraccording to claim 6 of the present invention is provided, in which amulti-layered film which at least two types of substances havingdifferent refractive indices respectively are synchronously depositedwith a constant periodic length is formed on a substrate, and themulti-layered film on the substrate is locally scraped in order tocorrect a phase of a reflective wave front in a reflective surface,wherein a scraping amount of the multi-layered film is determined sothat a phase combining a phase of the reflective wave front, which ismodified by a deformation of the substrate caused by scraping themulti-layered film, and a phase of the reflective wave front, which ismodified by locally scraping the multi-layered film, becomes equal to adesirable correcting amount.

[0033] According to the claim 6 of the present invention, since ascraping amount is determined based on a phase of a reflective wavefront which is modified by a deformation of the substrate caused byscraping the multi-layered film, the reflective wave front can becontrolled with a high precision after scraping the multi-layered film.

[0034] Also, the method for manufacturing a multi-layered filmreflection mirror according to claim 7 is provided, in which themulti-layered film may comprise a layer containing a Mo and a layercontaining a Si.

[0035] According to the claim 7 of the present invention, a phase of thereflective wave front of the reflection mirror having a largereflectivity in a wavelength band of 12.5 nm to 14 nm can be controlledwith a high precision.

[0036] Also, the method for manufacturing a multi-layered filmreflection mirror according to claim 8 is provided in which a substancecontaining Si may be formed on a reflective surface of the substratefrom which the multi-layered film is scraped.

[0037] According to the claim 8 of the present invention, it is possibleto prevent the oxidation of a layer except the Si layer. So, thereflective wave front can be controlled with a high precision afterscraping the multi-layered film while the change in characteristics ofthe reflection mirror due to oxidation is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1A and 1B are cross-sectional drawings showing amanufacturing process for a multi-layered film reflection mirroraccording to an embodiment of the present invention.

[0039]FIG. 2A to 2C are cross-sectional drawings showing a manufacturingprocess for a multi-layered film reflection mirror according to anotherembodiment of the present invention.

[0040]FIG. 3A to 3C are cross-sectional drawings showing a manufacturingprocess for a multi-layered film reflection mirror according to anotherembodiment of the present invention.

[0041]FIG. 4A to 4C are cross-sectional drawings showing a manufacturingprocess for a multi-layered film reflection mirror according to anotherembodiment of the present invention.

[0042]FIG. 5 is a cross-sectional drawing showing a manufacturingprocess for a multi-layered film reflection mirror according to thefirst example of the present invention.

[0043]FIG. 6 is a cross-sectional drawing showing the second example ofthe present invention.

[0044]FIG. 7 is a cross-sectional drawing showing the third example ofthe present invention.

[0045]FIG. 8A, 8B are cross-sectional drawings explaining a principlefor controlling a wave front by scraping a multi-layered film.

[0046]FIG. 9A to 9C are cross-sectional drawings explaining a method forcontrolling the reflection wave front by a conventional multi-layeredfilm scraping.

BEST MODE FOR CARRYING-OUT OF THE INVENTION

[0047] Reference will be described in detail with reference to drawings.Here, the drawings described-below are schematic drawings and the ratioof a thickness of a substrate to a periodic length of a multi-layeredfilm, a scraping amount of a multi-layered film, and the like are notalways correct.

[0048]FIG. 1A and 1B are cross-sectional drawings showing amanufacturing process for a multi-layered film reflection mirroraccording to an embodiment the present invention.

[0049] As shown in FIG. 1A, a Mo/Ru/Mo/Si multi-layered film 11 isformed on a plane substrate 13. The multi-layered film 11 is composed oftwo types of substances (two types of substances comprising ofMo/Ru/Mo-and Si) having different refractive indices respectively whichare deposited alternatively with a constant periodic length. On theforming the multi-layered film, an ion beam is irradiated after formingeach Mo layer. The multi-layered film has an internal stress of +14 MPa.

[0050] Since such internal stress is about {fraction (1/30)} of that ofa conventional multi-layered film which has an internal stress of −450MPa (compressive), the deformation in the substrate caused by the formedmulti-layered film is so small that the shape of the substrate can beassumed to be a plane even if the multi-layered film is formed.

[0051] The Mo/Ru/Mo/Si multi-layered film is composed of 50 layer pairshaving a period length of 6.8 nm and Γ 0.35, and 10 layer pairs having aperiod length of 6.8 nm and Γ of 0.1 which are formed on the Mo/Ru/Mo/Simulti-layered film. The multi-layered film is formed by an ion beamsputtering method. The Γ is a division ratio of a layer structure unit,and shows a ratio of a thickness of a substance having a largerabsorbance to a period length. Here, it is a ratio of a sum of athickness of the Mo layer and a thickness of the Ru layer to theperiodic length. The reason why the 10 layer pairs having Γ of 0.1 areformed on the most upper surface is to improve the control precision forthe wave front subjected to a scraping process of the multi-layeredfilm, as similar to the conventional embodiment as shown in FIG. 9.Since optical constants of Mo and Ru in a wavelength in the vicinity of13 nm are nearly, the effect of controlling the wave front by thescraping process of the Mo/Ru/Mo/Si multi-layered film is similar tothat of the Mo/Si multi-layered film. By scraping one layer pair fromthe multi-layered film, the optical path length is lengthened with 0.05nm, so the reflective wave front is delayed with 0.1 nm at both ofincidence and reflection. Therefore, as shown in FIG. 1B, if a part 17of the multi-layered film is scraped off, it is possible to control ashape of the reflective wave front with a high precision by adjustingthe scraping amount in the reflective surface. In addition, stress ofthe Mo/Ru/Mo/Si multi-layered film is so small that the shape of thesubstrate is not deformed by the unevenness in the total stress so as tobe kept plane even if the multi-layered film is locally scraped off.Accordingly, the scraping process of the multi-layered film enables tocontrol the reflective wave front with a high shape precision.

[0052] Next, a process for manufacturing a multi-layered film reflectionmirror according to another embodiment of the present inventionreferring to FIG. 2 to FIG. 4.

[0053] In FIG. 2, from a substrate 23 (FIG. 2A) on which a Mo/Simulti-layered film 21 is formed, a part 27 of the multi-layered film 21is scraped in order to control a wave front (FIG. 2B). In this state,the scraped film has a compressive stress so that a part of thesubstrate where the film is scraped off is deformed to concave. Then, inorder to cancel the deformation, another multi-layered film 25 is formedon a back surface of the substrate so as to produce a deformationcapable of canceling the deformation caused by the scraping process(FIG. 2C). Thus, the shape of the substrate is kept the shape before themulti-layered film is locally scraped off. While the multi-layered filmis formed on one surface of the substrate in the above-describedexample, the present invention will be applied to the case that themulti-layered films are formed on both surfaces of the substrate. And,in the present embodiment, while a multi-layered film is formed on aback surface of a reflective surface, a single-layer film may be formedon a back surface of a reflective surface if the distribution of thetotal stress in the surface is approximately similar to that on asurface.

[0054] In FIG. 3, Mo/Si multi-layered films 31 and 35 are formed on bothsurfaces of a substrate 33, respectively (FIG. 3A). A part 37 of themulti-layered film 31 is scraped in order to control the wave front(FIG. 3B), and then a part 39 of the multi-layered film 35 on the backsurface is scraped with the same distribution as that of themulti-layered film 31 on the surface (FIG. 3C). As the result, thedistribution in the total stress of the multi-layered film on thesurface is canceled with that on the back surface even after themulti-layered film is scraped off, whereby the substrate is notdeformed. Therefore, the reflective wave front can be controlled with ahigh precision.

[0055] In FIG. 4, Mo/Si multi-layered films 41 and 45 are formed on bothsurfaces of the substrate 43, respectively (FIG. 4A). In thisembodiment, based on the deformation of the substrate caused by thetotal stress distribution in the wave front surface due to the scrapinga part 47 of the multi-layered film 41, the scraping amount of themulti-layered film 41 is determined (FIG. 4B). In the case of a Mo/Simulti-layered film, since a part of the substrate where the film isscraped off is deformed to concave (FIG. 4C), the scraping amount of themulti-layered film is reduced compared with that of the case that thereis no substrate deformation.

[0056] That is, when a part of the substrate where the film is scrapedoff is deformed to concave, the scraping amount of the multi-layeredfilm is determined based on a phase of a reflective wave front in thereflective surface which is modified by the substrate deformation.Accordingly, the phase combining the phase of the reflection wave front,which will be modified by the substrate deformation, and the phase ofthe reflection wave front, which will be modified by scraping the partof the multi-layered film, becomes equal to a desirable correctingamount.

[0057] And, in the above-described method for manufacturing amulti-layered film reflection mirror, it is preferable that a substancecontaining Si is formed on a reflective surface of a substrate afterscraping the multi-layered film for wave front control. Hereby, anoxidation of the layer except the Si layer can be prevented. So, thechange in the property of the reflection mirror due to the oxidation canbe prevented, and the reflection wave front can be controlled with ahigh precision by scraping the multi-layered film.

EXAMPLE 1

[0058] A first example according to the present invention will bedescribed referring to FIG. 5. On a substrate 53 made of the low thermalexpansion glass processed to aspheric, a Mo/Ru/Mo/Si multi-layered film51 is formed. At the forming the multi-layered film, an ion beam isirradiated after forming each Mo layer. The stress of the multi-layeredfilm is +14 MPa or less. Concerning the irradiation condition of the ionbeam in order to achieve to have such low stress, for instance, an ionsource is Argon (Ar⁺), an acceleration voltage is 600 v, an ion currentdensity is 0.5 mA/cm², and an ion beam irradiating time is 2 second,preferably. Incidentally, the stress in the multi-layered film isevaluated by using a deformation amount of the Si wafer substrate, whichis caused by the film forming on the wafer.

[0059] The stress of the multi-layered film is about {fraction (1/30)}of that of a conventional Mo/Si multi-layered film which has an internalstress of −450 MPa (compressive), and other components except for thecomponent which causes a change in the radius of curvature of thesubstrate among the component which causes a deformation of thesubstrate by the multi-layered film forming is very little. As for thereason, it is confirmed by the calculation of the substrate deformationsimulation using the finite element method. The shape precision of theaspheric surface of the substrate after forming the multi-layered filmis 0.5 nm RMS.

[0060] The multi-layered film is composed of 50 layer pairs having aperiod length of 6.8 nm and Γ of 0.35, and 10 layer pairs having aperiod length of 6.8 nm and Γ of 0.1 which are formed on the formermulti-layered film. The multilayered film is formed by an ion beamsputtering method. According to the result of measurement of the wavefront, the reflective wave front is needed to delay at a part in theright side of the figure. Then, the most upper layer having Γ of 0.1 isscraped off with controlling the scraping amount. By scraping a part 57of the multi-layered film, the shape precision in the reflective wavefront is reduced to 0.15 nm RMS. Also, since the Mo/Ru/Mo/Simulti-layered film has small stress, even if the part of themulti-layered film is scraped off, the substrate deformation caused bythe unevenness of the total stress is not occurred. So, the scrapingprocess of the multi-layered film makes it possible to control thereflective wave front with a high precision. The fact that theMo/Ru/Mo/Si multi-layered film has a small stress is confirmed byevaluation of the deformation amount of the wafer substrate caused byforming a Mo/Ru/Mo/Si multi-layered film on the silicon wafer.

[0061] In the present example, the multi-layered film is scraped off bymeans of an ion beam irradiation. Concerning the ion beam irradiationcondition at this time, for instance, an ion source is Argon (Ar⁺), theacceleration voltage is 600 V, an ion current density is 0.5 mA/cm², andion beam irradiating time is 2 second, preferably.

[0062] In the present example, the Mo/Ru/Mo/Si multi-layered film inwhich an ion beam is irradiated after forming each Mo layer is used as amulti-layered film having a low stress, and the kinds of themulti-layered film is not limited by this and may be a multi-layeredfilm having a high reflectivity in a wavelength of 11 to 14 nm and asmall stress. The stress in the multi-layered film is whethercompressive stress or tensile stress and maybe 50 MPa or less,preferably. Because, when the stress in the multi-layered film is over50 MPa, the deformation component which can not be canceled by adjustingthe distance between the mirrors will be 1 nm or more thereby to affectthe EUV lithography.

[0063] And, in the present example, while the multi-layered film isscraped by irradiation of an ion beam, the multi-layered film scrapingmethod is not limited by this. As another multi-layered film scrapingmethod, a dry etching method or a method using an abrasive may beemployed when a desirable scraping amount can be obtained at any portionon the multi-layered film.

EXAMPLE 2

[0064] A second example according to the present invention will bedescribed referring to FIG. 6. On a surface and a back surface of asubstrate 63 made of a low thermal expansion glass processed toaspheric, Mo/Si multi-layered films 61 and 65 are formed, respectively.The shape precision of the aspheric substrate is 0.5 nm RMS. Here, sincethe multi-layered films are formed on both surfaces of the substrate,the substrate deformation caused by the stress in the multi-layered filmat the surface is canceled with that on the back surface of thesubstrate, so that the shape precision of the substrate is kept. TheMo/Si multi-layered film is composed of 50 layer pairs having a periodlength of 6.8 nm and Γ of 0.35, and 10 layer pairs having a periodlength of 6. 8 nm and Γ of 0.1 which are formed on the formermulti-layered film. The multi-layered film is formed by an ion beamsputtering method. According to the result of the measurement of thewave front, the reflective wave front is needed to delay at a part inthe right side of the figure. Then, the most upper layer having Γ of 0.1is locally scraped off with controlling the scraping amount. By scrapinga part 67 of the multi-layered film, the shape precision in thereflection wave front can be reduced to 0.15 nm RMS. However, since theMo/Si multi-layered film has a compressive stress of −450 MPa, the totalstress in the multi-layered film 61 becomes uneven after scraping a partof the multi-layered film locally and the shape of the substrate isdifferent from that before the scraping process. In order to cancel thedifference, a part 69 of the multi-layered film on the back surface ofthe substrate is also scraped at portions correspondent to the scrapedpart 67 of the multi-layered film on the surface of the substrate. Thefilm thickness distribution of the scraped multi-layered film on theback surface coincides with the total film thickness distribution of themulti-layered film 61 on the reflective surface. Accordingly, the totalstress produced on the reflective surface of the substrate is canceledwith the total stress produced on the back surface thereof, so that thesubstrate 63 is not deformed to be able to control the reflective wavefront with a high precision.

[0065] In the present example, while the Mo/Si multi-layered film havinga compressive stress is formed on the back surface of the reflectivewave front, the multi-layered film on the back surface is not limited bythe Mo/Si multi-layered film even if the total stress distribution inthe back surface is almost the same as that at the surface. Also, it maybe a single-layered film. And, in the present example, while a filmhaving a compressive stress is formed on the back surface, a film havinga tensile stress such as Mo/Be multi-layered film may be used. In thiscase, the film thickness is controlled by the reverse order in the caseof the film having a compressive stress. And, the scraping process ofthe multi-layered film may start from either the surface of thesubstrate or and the back surface thereof. And, in the present example,while the multi-layered film is formed by an ion beam sputtering, themulti-layered film forming method is not limited by this method, and amagnetron sputtering method or a vapor deposition method may be used.

EXAMPLE 3

[0066] A third example according to the present invention will bedescribed referring to FIG. 7. A Mo/Si multi-layered film 71 formed on areflective surface of a substrate 73 made of the low thermal expansionglass has a same structure as that of the multi-layered film of thesecond example, and will not be explained in detail. According to theresult of the measurement of the reflective wave front of the substrate,the wave front is needed to delay with most 0.6 nm at the part in theright side of the figure. Then, 4 layer pairs are scraped from a part 77of the multi-layered film in the right side of the figure. Hereby, theoptical length of a EUV light beam to the scraped part 77 of themulti-layered film is 0.2 nm longer than that before scraping. And, thereflective light is passed to the part 2 times of the incidence and thereflection so that the wave front is delayed with 0.4 nm. On the otherhand, locally scraping the multi-layered film produces an in-planedistribution of the total stress in the Mo/Si multi-layered film. Sincethe Mo/Si multi-layered film has a compressive stress, a part of thesubstrate where the film thereon is scraped is deformed to concave tothe bottom direction in the figure. The deformation amount is 0.1 nm inthe present example. Due to the deformation also, the wave front isdelayed at the part where the multi-layered film thereon is scraped. Thedelay is 0.2 nm, in the example. So, in the present example, as theresult that 4 layer pairs of the multi-layered film is scraped, by usingthe variation in the optical length by scraping the multi-layered film,and the variation in the substrate shape by locally scraping themulti-layered film, the needed delay of the wave front of 0.6 nm can beachieved, so a desirable precision of the reflective wave front can beobtained.

[0067] As mentioned above, while the methods for manufacturing amulti-layered film reflection mirror according to the embodiment of thepresent invention have been described, the present invention is notlimited by this and may add various changes in the range which does notdeviate from the point of this invention.

[0068] As previously described, according to the present embodiments andexamples, in a method manufacturing for a multi-layered film reflectionmirror is provided, in which one layer pair is scraped from the film oneby one in order to correct a shape of a reflective wave front, theinfluence of the substrate deformation caused by the scraping the filmhaving an internal stress can be suppressed. As the result, the shape ofthe wave front can be corrected with a higher precision to reduce thewave front aberration, whereby the focusing property can be improved.

We claim:
 1. A method for manufacturing a multi-layered film reflectionmirror, in which a multi-layered film which at least two types ofsubstances having different refractive indices respectively aresynchronously deposited with a constant periodic length is formed on asubstrate, and the multi-layered film on the substrate is locallyscraped in order to correct a phase of a reflective wave front in areflective surface, wherein said multi-layered film has an internalstress of 50 MPa or smaller.
 2. The method for manufacturing amulti-layered film reflection mirror according to claim 1, wherein themulti-layered film is a film which Mo/Ru/Mo/Si layers are deposited, andan ion beam is irradiated to a surface after forming each Mo layer.
 3. Amethod for manufacturing a multi-layered film reflection mirror, inwhich a multi-layered film which at least two types of substances havingdifferent refractive indices respectively are synchronously depositedwith a constant periodic length is formed on a substrate, and themulti-layered film on the substrate is locally scraped from in order tocorrect a phase of a reflective wave front in a reflective surface,wherein a film or a multi-layered film is formed on a back surface ofthe substrate in order to produce a deformation of the substrate capableof canceling a deformation of the substrate caused by scraping themulti-layered film.
 4. A method for manufacturing a multi-layered filmreflection mirror, in which a multi-layered film which at least twotypes of substances having different refractive indices respectively aresynchronously deposited with a constant periodic length is formed on asubstrate, and the multi-layered film on the substrate is locallyscraped from in order to correct a phase of a reflective wave front in areflective surface, wherein a multi-layered film having an approximatelysame structure as that of the multi-layered film formed on the surfaceof the substrate is formed on a back surface of the substrate, and themulti-layered film formed on the back surface of the substrate islocally scraped at portions correspondent to the portions where themulti-layered film on the surface of the substrate is locally scraped inorder to correct a phase of a reflective wave front with a samethickness as that of the scraped multi-layered film on the surface ofthe substrate.
 5. A method for manufacturing a multi-layered filmreflection mirror, in which a multi-layered film which at least twotypes of substances having different refractive indices respectively aresynchronously deposited with a constant periodic length is formed on asubstrate, and the multi-layered film on the substrate is locallyscraped in order to correct a phase of a reflective wave front in areflective surface, wherein a scraping amount of the multi-layered filmis determined based on an influence in a deformation of the substratecaused by scraping the multi-layered film.
 6. A method for manufacturinga multi-layered film reflection mirror, in which a multi-layered filmwhich at least two types of substances having different refractiveindices respectively are synchronously deposited with a constantperiodic length is formed on a substrate, and the multi-layered film onthe substrate is locally scraped in order to correct a phase of areflective wave front in a reflective surface, wherein a scraping amountof the multi-layered film is determined so that a phase combining aphase of the reflective wave front, which is modified by a deformationof the substrate caused by scraping the multi-layered film, and a phaseof the reflective wave front, which is modified by locally scraping themulti-layered film, becomes equal to a desirable correcting amount. 7.The method for manufacturing a multi-layered film reflection mirroraccording to one of claims 1 to 6, wherein the multi-layered filmcomprises a layer containing a Mo and a layer containing a Si.
 8. Themethod manufacturing for a multi-layered film reflection mirroraccording to one of claims 1 to 7, wherein a substance containing Si isformed on a reflective surface of the substrate from which themulti-layered film is scraped.